This invention relates to improvements in means and metods for providing sprocket wheel assemblies which afford optional drive characteristics. The apparatus of the invention has a particularly advantageous application for use in bicycles and will be so described. It is to be understood, however, that the application of the invention is not so limited and such is not intended.
Most of the present day bicycles embody a plurality of gears in the form of sprockets and utilize a chain drive which may be selectively shifted from one drive sprocket to another to permit one to pedal at different speeds or with the same ease and at a selected speed whether moving over a flat surface or up or down an inclined surface.
In accordance with the prior art, the plurality of the drive sprockets embodied in a drive system for a bicycle are normally fabricated separately and then bolted or otherwise secured together in a side-by-side relation in the mounting thereof to form part of the pedal assembly of a bicycle. The construction and assembly of drive sprockets in this fashion has proven to be relatively costly procedure, in terms of both material and labor. In mounting the various drive sprockets of an assembly their sprocket teeth must be precisely formed, related and oriented to enable a smooth and certain shifting of a drive chain from one to another in their use. This means that not only must each sprocket be carefully machined but the drive sprockets of any assembly must be carefully oriented as they are assembled to a pedal structure and they must thereafter remain fixed in their established positions. Achieving these objectives with any great degree of certainty is extremely difficult since it requires that not only the sprockets but their fastening means must be designed with careful tolerances to insure that in the final assembly the sprockets are established in a proper parallel relation and with the precise spacing required for their effective use. Further problems are inherent in this prior art practice of providing sprocket assemblies in that the vibration and shock to which a bicycle is subjected during any normal usage will tend to loosen and consequently produce a misalignment of parts, resulting in wear on the parts. It will be obvious, of course, that where the parts become misaligned due to loosening of their fastening means that malfunction in the process of shifting gears in a bicycle can readily occur. The same may occur where there has been wear in use and even with maintenance to tighten the drive sprocket assembly there is an inherent altered alignment.
Additional complications have been produced in prior art sprocket assemblies in the conventional fastening in connection therewith of a chain guard. The chain guard itself is often subject to impact in handling of a bicycle, which impact can in turn affect the security of the fastening means by which it is incorporated in conjunction with the sprocket wheel assembly. The indirect result of such an impact can be a loosening of the parts of the sprocket wheel assembly or a misalignment thereof due to the fact that the rigidity of the assembly, being comprised of separable parts, is not such to offer optimal resistance to displacement of parts under such conditions.
It is to the solution of the noted problems of the prior art to which the present invention is directed.